The present invention relates to a method for judging load distribution by the every wheel of a vehicle or the load distribution by every axle and a device thereof, and a judgment program of the load distribution of a vehicle.
When the pressures of tires mounted on a vehicle are decreased, a fuel mileage is deteriorated and there is danger of provoking burst at high speed running. When a tire is deflated, the decrease in pressure is detected through utilizing the change of properties of tires such as the decrease of the dynamic load radii of tires and the change of resonance frequency.
For example, a conventional detecting device for the decreased tire pressure uses a principle that since the outer diameter of a tire (the dynamic load radius of a tire) is reduced more than that of a tire having normal inner pressure when the pressure of a specific tire of a vehicle is reduced, rotational angular velocity is increased as compared with other normal tires. For example, a method for detecting the decrease in inner pressure from the relative difference of the rotational angular velocities of tires uses a value obtained from following formula as a judging value;DEL={(F1+F4)/2−(F2+F3)/2}/{(F1+F2+F3+F4)/4}×100(%)(Japanese Unexamined Patent Publication No. 305011/1988). Herein, F1 to F4 are the rotational angular velocities of a front left tire, a front right tire, a rear left tire and a rear right tire, respectively.
However, since the fore-mentioned properties of tires are changed by the change of loads such as the number of passengers on board and the weight of a load, the change of a load is judged as the change of tire pressures in the case the change of a load cannot be distinguished from the change of tire pressures; therefore the decrease in pressure cannot be accurately judged.
When all of tire pressures are normal, the fore-mentioned judging value DEL is zero, but when deflation is generated for a wheel, the judging value is changed in accordance with the level of a dynamic load radius. When the decrease in pressure at which an alarm is to be issued to a driver is 30% deflation relative to the normal pressure, the judging value at 30% deflation is referred to as a threshold, and the alarm is issued when the judging value exceeds the threshold. However, the larger the load is, the smaller the decreased level of the dynamic load radius at deflation is; therefore the judging value at 30% deflation in the case of one person boarding is larger than the judging value at 30% deflation in the case of 5 persons boarding.
For example, the judging value at 30% deflation is to be 0.3 in the case of one person boarding and 0.25 in the case of 5 persons boarding. In this case, when an alarm is designed to be issued at 30% deflation in the case of 5 persons boarding, the threshold must be 0.25. However, when the threshold is 0.25, an alarm is issued at 25% deflation in the case of one person boarding (30×0.25÷0.3=25).
There are inventions described in Japanese Unexamined Patent Publication No. 23425/1999, Japanese Unexamined Patent Publication No. 189136/1999 and Japanese Unexamined Patent Publication No. 306093/2003 as a device for judging the load distribution. In Japanese Unexamined Patent Publication No. 23425/1999, a means of detecting resonance level is required. In Japanese Unexamined Patent Publication No. 189136/1999, a means of detecting brakeage force and a means of calculating the gradient μ of road surface are required. In Japanese Unexamined Patent Publication No. 306093/2003, a means of detecting acceleration and deceleration is required.
It is described in Japanese Unexamined Patent Publication No. 196791/1997 and Japanese Unexamined Patent Publication No. 115578/1998 that the information of the load distribution is utilized for detecting the decreased tire pressure. In Japanese Unexamined Patent Publication No. 196791/1997, a load is detected by using a suspension stroke sensor. In Japanese Unexamined Patent Publication No. 115578/1998, a load is detected by judging the change of resonance frequencies before and after opening or closing a door, a trunk or a fill opening as the change of a load, or using a suspension stroke sensor.
Further, it is described in Japanese Unexamined Patent Publication No. 2222/1997 that a ratio of the rotational speed of front wheels to the rotational speed of rear wheels is changed at brakeage and at no brakeage, but relation between the ratio of the rotational speed of front wheels to the rotational speed of rear wheels under brakeage and the load of a vehicle is not described.